I'll try to keep this as short and concise as possible. I'm in over my head and would sure appreciate some advice from the knowledgeable people on this forum. I'm not even sure I'm in the correct category so moderators feel free to move this post.

We have a 2002 "gearless" eight color flexographic press from Italy. I was placed in charge of the facility near the end of the installation process for this press. I actually showed up the day the power was connected for the first time. The press would not come on. What followed was several hours of the finger pointing and yelling in Italian and English. Our press manager at the time had decided that the newly increased power service that the local utility had installed would provide stable "clean" power. As far as the new press was concerned, the power was not "clean" enough. It was eventually decided that we needed an isolation transformer so one was purchased that day and installed the next day. The second time the power was applied, the press started up and production testing began a few days later.

This press has a Xycom HMI running Windows NT and Wonderware. The unwind and rewind stations are controlled by Siemens OP17 panels that communicate with the Siemens S7-400 PLC in the upper deck's electrical cabinet. The S7-400 communicates via a Profibus link to the heart of the press, a Rexroth Indramat servo drive system. Specifically The brains of the press is the Indramat CLC-D02.3 along with eight HDS drives and four HDD drives that control the 20+ Indramat motors on the press.

After nearly 42,000 hours of nearly flawless operation, I'm failing Indramat HDS drives like crazy. Five have failed in the last few months. The error codes may start out as Fiber Optic Ring Not Closed or Drive Address Not Correct on the CLC and sometimes we can re-start and clear the Watchdog on the HDS drive but not for long. Sometimes we can run for about 24 hours before the drive fails again but usually it's a shorter period of time. The HDS drives are now $5,500.00 each and getting harder and harder to find.

After doing a great deal of reading and talking to the folks at the press company and at Bosch Rexroth Indramat, I've concluded that there are two primary issues.

First, our power supply is not very good. Even a very brief power sag or flicker of the lights shuts down the press. We do not have a UPS system on the power supply to this press although I've pushed for one many times. The owners of the company have always felt that the fact that the isolation transformer allowed the press to start up in 2002, means that it must have "cleaned up" the power. I've tried to explain that the isolation transformer is not a surge protector and it is not a voltage regulator. It may act as a partial filter that cuts out some of the interference coming from the "street power" but it's primary function is largely related to it's name.

The second issue that I'm dealing with is a search for the grounding layout for the power coming into this press and the press itself. The day the isolation transformer was installed, no thought was given to how it was going to change the grounding of the system. As I understand it, the isolation transformer broke the link from the press to the ground in the power supply system. My research indicates that a poor grounding situation can play havoc with these modern servo drive machines.

Am I on the right track here? Any thoughts or comments would be greatly appreciated.

 

It is impossible to give any specific advice without completely reviewing the system, but I have seen many "bad power" problems vastly improved by driving a copper ground rod into the earth and grounding the electrical panel to the earth ground. You might also talk to the Psytronics folks, their 3 phase power filters are routinely specified by the major automotive companies for their control panels.

Bill Sturm

 

Responding to Astixjr's 20-Jul-09 (00:55) post... Following are a few questions, that may be helpful in "pointing" you in a direction to the solution:

1) What is kVA capacity of your plant's utility tranformer.

2) What are the "true" ph-to-ph voltages at: a) source bus; b) input terminal of VFD drive; and c) output terminal of VFD drive (or motor terminals)?

3) What are the "true" ph-neutral voltages for each of the locations shown in 2)?

4) What are the "true" ph-ground voltages for each of the locations shown in 2)?

5) What are the "true" line currents for each of the locations shown in 2)?

Regards, Phil Corso (cepsicon [at] aol.com)

 

I have also seen in a printing environment that the Indramat drives just fail at a high rate. Capacitor problems, etc. Typical was shut it down for a weekend and replace a couple drives to get it running. Sometimes a heat gun would get them to finish booting.

Raise Cain with the press manufacturer, they have more pull with Indramat or whoever owns the brand. Don't buy the "your fault" argument. Suggest that the next press will be from a competitor. We chased the power thing for a while. It doesn't explain why some drives fail and some last the distance.

Regards
cww

 

Thanks for the input guys, it has been very helpful. My delayed response is due to the fact that in the process of trying to answer some of the questions asked and respond to the comments in this thread, things got a bit more confusing. To start off, the local utility offered to come out and install some recording monitors. One was placed on the main power inside the printing press and the other was installed on the power service outside of our building. While waiting for a two week period to go by, my electrical contractor came out to look at some other issues. We shut down and took the cover off of the isolation transformer. For some reason, the former press room manager pulled from the -5% Volt tap on the transformer. So even though the press manual shows the system setup to take 480 Volts, we have started out by feeding it 457 Volts. When checked, we did have exactly 480 Volts into the isolation transformer.

Also, the ground line from the press electrical cabinet comes into the transformer and runs in the bottom of the case to share a case ground with the incoming ground/neutral from the 200 Amp service box. The XO lug on the Iso. Trans. is empty. Even before the electricians got there, the utility guys suspected we would find exactly this situation based on readings they took when the installed the monitor. The electricians wanted to look at the main power box inside our building and in doing that they noted two conduits were very warm as they came out of the supply panel. A quick test of the Amps showed one of them going to the water line was 27 to 30 Amps and the ground going up into the metal roof structure was reading 40 to 46 Amps. Fun. After several days of looking for the problem inside the building, the utility company tech found the issue when he came out two weeks later to download the power monitor memory cards. We a have three wire three phase power supply and one of the grounded legs had come out of the grounding block just below the weather head. We shut down right away and they fixed the problem. Unfortunately, the tech installed the monitor incorrectly outside the building so that data was useless. We only had our first power interruption today so with any luck, the recorder inside the printing press collected the data. It was just a flicker of the lights but it shut off the press that was running at 500 fpm. Fun.

The Psytronics folks have been very helpful, thanks for that lead. It's not Bosch Rexroth Indramat's fault. We have been feeding the press "dirty" power for seven years. The Iso. Trans. is probably not really the device we needed in the first place and it's clearly wired wrong. Also our grounds have probably been bad for years, both at the press and in the building in general. Its our fault. We let the former press manager jury rig the entire operation for over ten years. Now we are paying the price. Actually, so is he. He's got two years left on a five year Federal drug charge sentence. Maybe he can spend some time in the prison library, reading up on industrial power applications.

Thanks guys.
Astixjr